The present invention relates to a dust guard for a scroll chuck for use in holding a work in a machine tool or the like.
It is known to use a scroll chuck in a machine tool such as a lathe, a milling machine or a drilling machine. The prior art scroll chuck comprises a main body having a plurality of chuck slots radially formed in its surface, a chuck jaw slidably fitted in each of the chuck slots and consisting of a master jaw and a top jaw, and a scroll plate accommodated in the main body and provided with a scroll thread on its front surface for engaging with a rack provided on the rear surface of each chuch jaw. All jaws are adapted to radially move in or out simultaneously because of the provision of a bevel pinion engaging with a bevel gear provided on the lower surface of the scroll plate.
When the chuck jaws are disposed at or near the inside or outside limit of their radial travel, a large portion of the scroll thread is left unoccupied by the chuck jaws and exposed to the ambient air through the chuck slots. The onerous problem involved in this condition is that chips fall into the chuck slots and stick between the flanks of the scroll thread. Therefore, when the scroll plate is turned after a cutting operation and the chip-clad portion of the scroll thread comes into mesh engagement with the rack provided on the lower surface of each chuck jaw, it becomes difficult to turn the scroll plate further. Thus the prior art scroll chuck has a disadvantage that more effort is required to move the chuck jaws after a cutting operation. The prior art scroll chuck has another disadvantage that it is very difficult to remove the chips from between the flanks of the scroll thread because the chuck slots are so narrow that most of the scroll plate is hidden by the main body.
A dustproof cover or covers to keep chips and dirt out of the chuck slots may be provided as an attempt to solve the above problem. However, such a cover or covers cannot but be of a complicated and expensive nature because they have to meet the structural requirement for providing the chuck jaws with radial movability.